Expanded – threaded – driven – headed – tool-deformed – or locked-thr – Externally threaded fastener element – e.g. – bolt – screw – etc. – Pilot end having means enhancing fastening or installation
Patent
1996-12-26
1998-05-12
Wilson, Neill R.
Expanded, threaded, driven, headed, tool-deformed, or locked-thr
Externally threaded fastener element, e.g., bolt, screw, etc.
Pilot end having means enhancing fastening or installation
411 29, 408231, F16B 2500, F16B 1304
Patent
active
057496897
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a drill with a drilling shank, particularly with a screw shank comprising a self-tapping thread, and with a fork-shaped hard-material plate-shaped drilling tip disposed opposite the driving end of the shank, said drilling tip being inserted into a holder in the shank, said holder comprising two grooves, disposed diametrically with respect to each other in the shank, for accommodating prongs of the drilling tip. Therefore, the drill may also and preferably be a drilling screw owing to the design of its shank with a self-tapping thread.
Such a drill provided with a drilling tip is described in U.S. Pat. No. 3,715,952. In said drill, the drilling tip is inserted into a continuous transverse slot provided at the drilling end of the drilling shank, said transverse slot ensuring that the drive is transmitted to the drilling tip and the root of said transverse slot forming the abutment for the absorption of the axial drilling force, since the drilling tip is supported in its central region against the root of the transverse slot. At its lateral edges, the drilling tip comprises arms that extend axially with respect to the drilling shank and which taper away from the drilling tip, said tapering obviously serving to facilitate the introduction of the arms into additionally provided axial grooves in the drilling shank, which grooves are wider than the transverse slot. Said arms each contact just one wall of the grooves on one side and are thus capable of helping to transmit the torque from the drilling shank to the drilling tip, this, however, being restricted to that region of the arms that is not tapered. The grooves serve further to remove drilling chips or other drilled-out material and therefore leave sufficient space free next to the arms of the drilling tip. The end of the drilling shank facing the drilling tip is, therefore, of relatively complex geometry with its transverse slot and the widened grooves opposite the drilling tip.
A different method of attaching a drilling tip to the drilling shank of a drilling screw is disclosed in DE-PS 4 003 374, which is based on the principle of holding an extension of the drilling tip, said extension emanating from the centre of the drilling tip and being force-fitted into a central recess in the end of the screw shank facing the drilling tip. The axial drilling force is transmitted from the end face of the extension onto the root of the recess. In order to increase the torque which is transmitted through the positive and non-positive connection between extension and recess, the drilling tip is provided, next to the extension, with strips that project from the cutting tip, said strips--as shown in FIG. 14 of the publication--engaging correspondingly shaped grooves in the relevant end of the screw shank. The two strips, just like the grooves, extend parallel to each other and are of a length corresponding approximately to the depth of the recess, the ends of the strips maintaining a small distance from the ends of the grooves, with the result that, therefore, the axial drilling force is absorbed by the end face of the extension via the root of the recess. This design, too, of the relevant end of the screw shank is relatively complex, since, apart from the recess, it additionally comprises the two grooves. The publication also describes a variant on the above-explained design according to FIG. 14, the upshot being that the two grooves are replaced by an annular shoulder as deep as the grooves, with the result that, at the relevant end of the screw shank, next to the recess, there remains an annular collar which embraces the recess and, in any angular position of the drilling tip with respect to the screw shank, is capable of accommodating the two strips of the drilling tip, which, however, are then hardly able still to transmit a torque for lack of lateral abutments. Torque can then only be transmitted through the force-fit of the extension in the recess. The above-described designs of the connection of a drilling tip
REFERENCES:
patent: 4480951 (1984-11-01), Regensburger
patent: 5184925 (1993-02-01), Woods et al.
patent: 5213459 (1993-05-01), Palm
patent: 5551818 (1996-09-01), Koppel
EJOT Verbindung Stechnik GmbH & Co. KG
Wilson Neill R.
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